The book deals with the most important cancer type in Iraq, breast cancer, particularly, the viruses that consider as one of the many causative agents specially the virus of mouse breast cancer (mouse mammary tumor virus), recently, it is thought that the 95% genomic similar to MMTV is the HMTV (human mammary tumor virus) may be interfering with human breast cancer pathogenesis. The research was conducted in Iraq and further research was in Dr.Beatriz Pogo Lab, supervised by Dr.Stella Melana at Mount Sinai Medical Center/ New York/ USA. By different molecular ways like quantification and qualification of DNA extracts, Nested PCR, Hybridization the HMTV detected in the Iraqi breast cancer samples. I hope the methods of the research will be very useful for researchers to conduct more papers about the viruses and breast cancer pathogenesis.